STEALTH POLYMERS
Not all the new nanobots will look like machines. For instance, the University of Michigan's James Baker developed a dendrimer (a complex polymer) to fight cancer. In rat trials, the dendrimer used folic acid to trick cancer cells into letting it in. The dendrimers also carried a potent chemotherapy drug, which then poisoned the cell before being flushed out of the body. Such targeted chemotherapy may prove both safer and more effective than current treatments.

The animation below shows the timecourse of the internalization of G5 dendrimer that is labeled with a green fluorophore (AlexaFluor 488) and targeted with an antibody (Herceptin). First you will see the binding to the cell membrane, then the dendrimer gets internalized into the cell. Images were taken every 10 minutes for 90 minutes (10 frames total, each shown for 1 sec). Click the image to activate the cell internalization movie. Images prepared by Jennifer Peters, Ph.D.

CLICK ON IMAGE TO SEE ANIMATION. Internalization of G5 Dendrimer into Cells, Prepared by Jennifer L. Peters, Ph.D., Michigan Nanotechnology Institute for Medicine and Biological Sciences

An artist's depiction of dendrimers floating with cells. Jolanta Kukowska-Latello, Michigan Nanotechnology Institute for Medicine and the Biological Sciences.

A simplified computer model of the U-M nanoparticle showing the dendrimer's branching structure and how molecules and drugs are attached. Jolanta Kukowska-Latello, Michigan Nanotechnology Institute for Medicine and the Biological Sciences.

Such materials merge with their human hosts, straddling the divide between the living and the inanimate. Things, it must be said, can get creepy. A UCLA team led by biomedical engineering professor Carlo Montemagno grew heart-muscle cells onto a gold and silicon structure. Using methods borrowed from computer chip makers, they first etched supporting "beams" into a thin block of silicon. They coated the surface with a biocompatible polymer and an arched layer of gold. Then they deposited living heart-muscle cells from a rat. After the replicating cells enveloped the gold, the polymer was dissolved and beams snapped off, and the microscopic device--an organic-inorganic hybrid--began to shuffle forward. "This device is alive," Montemagno says. Unsettling, right? But it's useful, too. This miniature Frankenstein is self-assembling and requires no power source other than the adenosine triphosphate (ATP) molecules that power living cells. The back-and-forth movement of many such biobots, grown from a patient's own shoulder muscle, might one day generate the electricity to power implants--perhaps helping paralyzed patients to breathe.

CLICK ON IMAGE TO SEE ANIMATION.
Size scale and creation of the muscle microbots; video of the actual bots moving at the end. UCLA Engineering

Musclebot in action. UCLA Engineering

NanOss, the material used in these orthopedic implants is made of hydroxyapatite--one of the major components of bones and teeth.

Tejal Desai investigates ways to reproduce the functioning of the pancreas, releasing insulin into the bloodstream as needed. The devices have been used with success in lab rats; similar devices could release other kinds of hormones to treat a variety of disorders.

One of the best established implant technologies is restoring hearing to tens of thousands of patients worldwide. Sound is converted into electrical signals and then transmitted to the auditory nerve, bypassing damaged structures in the ear. While it resembles a hearing aid, the cochlear implant interacts directly with the nervous system.

Nanotechnology, which ultimately could affect everything from computer hardware to space travel, may hold the greatest promise in medicine. A number of researchers anticipate using nano-size robots to scour arteries clean, to monitor blood chemistry, to deliver drugs to precise locations, and more. To make such nanobots move, scientists are considering bacteria as their models. Future devices could be driven by artificial flagella--an alternative vision has real bacteria attached to the end of a nanobot to provide propulsion.

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